Antenna arrangement



` March 6, 1945. A. ALFORD 2,379,628

' ANTENNA RRANGEMENT. l

Filed March 25, 1942 ATTa/NEY 'plane communication, etc.

Patented .Man 6, 1945 Andrew Alford, New York, N; Y., assigner to vFederal Telephone and Radio Corporation, a `cnr- Application March 2s, 1942, summa. 435,885-

15 claims. (creto-33) This invention relates to improvements in antenna devices, and in kparticular to .such arrangements Iasare used in .airplanes for .receiving horizontally polarized Waves from all directions. This is apreferred type antenna for radio range use lin accordance withl my application, Serial No. 303,206, led November "7, 1939, .in plane-tov Under these circumstances, there is no. particular :need for a completely `circular characteristic, nor lthat polarization be .only horizontal. Prime considerations are .rather that the .antenna be small, light, simple .and relatively rugged. v K

It is `accordingly an object .of the invention .to provide .an improved antenna meeting `the .above requirements. v f

Another `object is .to Aprovide .an improved type of ygenerally non-directional Aantenna for operal tion at relatively short `Wavelength.

A further object'is to provide 4an improved antenna, the performance of which Will .be relatively unaected by 4changing Weather conditions,

such as rain, ice vformation, etc.

are joined to eacl'liotherat'goneend. 4Ii farms Ill and -I'I vvere :to make `an angle of -`180" with respect to :each other, the resultant chara'cteristic of Athe antenna would :be in Vthe nature 'ofv a Y ligure of .18, :as obtained from a ydipole a half waveshown, this :angle is in the neiglxborhood fof '80.

This preferred 'angle .is the result yoi a vcornpromise, for `the less the spread fof .arms Is0 and .I;I the more the richaracteristic approaches circularity. However, `with 4such improvement in lthe characteristic the radiation resistance decreases and `proper tuning of the unit lbecomes more critical. Arms I0 :and .IfI- are Vsupported .by astrut -mernber I2 rigidly mountedto :the fuselage I3 of `the aircraft and .supporting arms I0 and I.I vsubstantially at their point of juncture. In order Other objects and further features of novelty.y

and invention Will hereinafter be `pointed vout or willbecome apparent to those .skilled .in the art from a reading of the following ,specification in connection with the drawingattached hereto. In .said drawng- Fig. 1 'is a plan View of apreferred embodiment of .the invention.;

Fig. 2 is a side elevation of the embodiment of Fig. 1.;

Fig. 3 is a Vgraphical representation of a .horizontal .characteristic of vthe antenna of Figs. 1

'Figs 1 and 2. According to this embodiment,

the antennacomprises two `radiating elements ID, II which .have a length preferably vone-'quarter the Wave-length at the operating frequency and that :the ,characteristic :of .the antenna may 'be essentially responsive to horizontally vpolarized energy, :arms :I0 and .II lie in a pla-ne which is normally horizontal, namely, a plane generally parallel yvvith the AWings of the. aircraft. Thus. the entire antenna vunit-comprisin, arms lII) and IfI .andsupport I2 maybe made as a sing-le Welded structure and-securely .fastened to the aircraft.

In :order suitably Eto couple the 4antenna velements IIJ, -II to Wave-translatingmeans withinthe aircraft (not shown), a pair of conductors I4.

I5 extend in insulated relation through a hollowed portion ofthe strut I2 .and pass :out .near the trailing edge thereof to be Aconnected respectively to arms .II and I0. Conductors I4 and I5. are connected to .arms II) vand II Yat points of juncture of these arms in order vthat an appropriatematch between theantenna impedance and the characteristic impedance of the transmission line formed .by conductors Il, I5` may be made.

In an :actual embodiment -fof the device jjust described which was designed `to operate at frequencies of 'theorderof 100 megacycles, the characteristic impedance of the line formed by con doctors-I4 and I'was 16,0 ohms, and a'spacing of six inches Was'ffound preferable as the vdis-l tance from the vertex of the V formed .by farms I0 and II to the kpoint of connection of conductors Hand ISYftoarmsI Iand I0. It is clear that with such a connection, the portion of arms In .and -:II extending out vfrom the point thereon at which the coupling conductors are connected, operate as an antenna, and the remainder of arms Ii) and II adjacent the vertex of the V operate as building-out sections for the abovenoted impedance-matching purposes. The characteristic of such an antenna is roughly shown by the diagram of Fig. 3 from which it may be seen that a minimum is obtained normal to the direction of fright, but that the ratio azb of.

maximum to minimum characteristic is of the order of 2.5:1. erally non-directional nature. It is to be noted that the pattern of Fig. 3 represents the characteristic of the antenna comprisingarms I and I I by themselves as energized. in the manner' indicated, that is, without considering any effects of the presence of the aircraft fuselagen I3. It is clear however that if the fuselage I3 is metallic, it

may act as an -attenuator in the general direction.

of flight to make the vratio of maximum to minimum characteristic approach 1:1. In thismanner, a lroughly circular characteristic is obtained This attenuating effect of the fuselage I3 of course depends largely upon the spacing between the antenna and the nearest conductive surface of the fuselage. As this spacing is decreased, the attenuating effect increases, and I have found that a very nearly circular characteristic may be obtained (with antenna arms a quarter wavelength longand an angle of .80 as above specied) when this spacing is inches or, more generally, when the spacing isabout 0.08 to 0.09 of a wave-length.

In order to promote rigidity of the antenna structure and to decrease its resistance to wind,

arms In and II are preferablyof streamline sec' ors I 4 and I5 are thus situated ysymmetrically with respect to ground potential (strut I2v and portions of arms I0, Il adjacent thereto), and, due to this fact, thelactive antenna elements I0,

The antenna is thus'of a genlength.

, to each other.

is not of metal so that it cannot be as good an attenuator of radiant energy in the direction of flight. In such case, I provide antennae as shown in Figs. 4 or 5.

The form shown in Fig. 4 comprises two arms 20, 2I again disposed so as to be normally horizontal in ight and each of overall length equal substantially-to a quarter of the operating wave- In this embodiment, however, each arm is formed with three straight sections at angles The entire antenna structure thus approximates the shape of a loop. Referring to Fig. 4a, the characteristic of the modincation of Fig. 4 is seen substantially to approach circularity.

In the further embodiment of Fig. 5, the antenna again comprises two arms 30, 3I, disposed f in a plane which is normally horizontal in iiight and substantially a quarter wave-length long. Arms 30, 3| are, however, provided with one less bent section than the arms of the antenna of Fig.v 4, for purposes of greater rigidity. It will be noted from th'e radiation characteristic for this latter form (see Fig. 5a) that there is a greater departure from ar circular characteristic and something half way between the characteristic of the V antenna of Fig. tained.

It is to be noted that the horizontal characteristic of an antenna of any of the above-described natures on an airplane is not a uniquely defined quantity because this characteristic is always a function of the angle of bank of the airplane.

, An approximation of the horizontal characteristic may be obtained if the airplane is flown in a large circle, that is, withoutv any appreciable bank, but best results may be obtained by flying over the same location from different directions while a received signal is being measured. If

' qualified with the statement that it is for a 30 II may be supported directly by means-of metaltion is perfectly satisfactory without any need of modification of the antenna or its connections at both 96 and 104 mc. `.The mismatches whichare introduced by a deviation in frequency from the frequency for which the antenna is designed to operate introduce losses affecting both the de- Sired signal and any noise picked up. When the losses thusintroduced are not very large, and the antenna is used for reception, the receiver automatic volume control is able to make u'pfor these small differences so' that' no appreciable effect is noted on the range of localizer or other Signals being picked up. 'f

Under certain circumstances, it may be desirable that the airplane antenna exhibit a still more nearly circular inherent radiation charac` teristic, such as for example, when the fuselage bank.

In the above discussion, reference was made to the compensation effect of a metallic fuselage' on the V antenna characteristic. The fuselage itself and not the wing is, of course, meant; and the resultant approximately circular characteristic thus obtained has reference to the usual flying conditions of zero bank. Since no means have been found for automatically compensating for the increased attenuating effect of the Y in this direction is below a tolerable minimum.

Inthe above described embodiments wherein the attenuating effect of the fuselage of the plane is relied upon to make the overall characteristic of the-antenna approximate circularity, it is to be understood that the antenna is placed on` the side of the airplane remote from the wing.

For example, if the airplane is a low-winged monoplane, the antenna should be mounted on top of the fuselage whereby the fuselage attenuation may predominate. If in this type plane l and circularity is ob-v theantenna 'be Amounted "below 4the fuselage wing `yhas a greater attenuating effect' ron characteristic normal-"to the direction Jof flight than the @fuselage -`has on I4the vcharacteristic in the direction of r4iligl'rt, thus yfinalizingr 40for lan leven greater' rati-o of Amaximum to kminimum vfclfraracteristic. n the other handyif the airplane be a 'high-winged lmonoplane, 'it is dpreferable install the antenna below :the fuselage whereby the `fuselage .attenuating Aeffect "may predominate to yield a characteristic approaching circularm. O course, `in the case of Aa center-winged craft', substantially 'no Adifference kin characteristic is obtained if the antenna be linstalled 'aboveor "below the 'fuselage It is clear that rI have described :anext'remely simple antenna device :suitable for ultra-shortwave use, whether for transmission Aor reception, and that with :relative ease, la Arelatively uniformly non-directional characteristic .may be obtained therewith. The structure exhibits electrical advantages in that it is relatively Iunaffected in its performancel under adverse weather conditions` `such as' in rain 'or when ice forms.r It is clear that lif any Aice should form, thisfformation would be on theleading .edge of 'members l0, Il and i2, particularly strut 12,`

and that under the circumstances, no additional of 'the same potential, .Aerodvynaxnicalln 'the structure has the advantages that it may .Lbe relatively easily adapted to streamlining and that there are few .parts to offer resistance to flight. From a structural point `of View as above 'in'di-v cated, the antenna may be made highly `rigid and strong with light-*weight materials. A preferred material from which Ato construct 4strut "L2 and arms l0 Aand Il .is.beryllium-coppery alloy sheet because of its highly excellent .resiliency and resistance to tiring 'in .the -`presence o'f yibration. Furthermore., as alsopointed outabove, rigidity is enhanced by the fact that .all structural `parts may be metallically interconnected.. the only required insulator being a't a point' of no structural stress.

Although I have described .the .above ,perferred embodiments of my .invention .as ncludingantenna arms of one or more straight sections, it is to be understood that curved members of approximately equivalent form may be employed to yield substantially equivalent characteristics. For example, the embodiment of Figl could 1include two continuously arcuate arms each a quarter wave-length long, and substantially the characteristic of Fig. 4a would result.

Furthermore, while I have described the V angle preferably to be substantially 80, vsatisfactory results may be obtained within as wide limits as 40 to 120. Satisfactory results may also be obtained by adjustment of the antenna between 0.07 and 0.15 of a Wave-length above the "What-is `claimed is: i A ffl. ian-'antenna arrangement having ya given radiation characteristic in a given plane, comprising Ia Isupjgiorting member, vtwo :arms 4forming a single V antenna in said planethe apex vof said V tenninatingon said member, said :arms being rigidly-connected 'to said supporting member toward-one-end thereof, 'and means for energi-'zing said arms.

2. #rnantenna arrangement having -a generally nondirectiona1 characteristic a given pla-ne V'comprising a supporting member, two oonv4ductive arms vof va 'length equal substantially to a quarter lwavelength at the 'operating frequency of jsaid antenna arrangement, said I'arms forming a single "V antenna extending Ain said plane, said arms v4being rigidly supported toward `one Vfend thereof Aat substantially the same point on said member, and ymeans for energizing Isaid Aarms at points lthereon equally spaced fromy the 'point of rigid support.

K B. An antenna'arr'angernent having ya generally non-directional characteristic in a given plane, comprising a. hollow supporting member, two conductive arms of a length 'equal Vsubstantially to a quarter wave-length at the operating frequency of said antenna arrangement, said arms forming a singleV antenna extending in said plane ,and

being rigidly connected to said` supporting member at substantially one .end thereof, and means for energizing said 'arms at points thereon equally spaced from the point .oi vrigid connection, said energizing Ameans including Within said supporting member conductor means `further extending from one end ofsa'id supporting member to said equally spaced points. y

4. An antenna arrangementaccording y13o-claim 3, wherein .said arms .are substantially straight. 5. An antenna arrangement `according to claim 3 wherein said arms are substantially straight and make an angle' 'less than y180" with veach other in .said plane.

.6. An antenna arrangement according'to claim 3, wherein said arms vvinclude .a portion on one fuselage, and of the point of connecting tithe. V

many modifications, additions and omissions may be made Within its scope as defined by the appended claims. I

arm making an angle less .than 'with a corresponding portion of vthe other arm.

7., An antenna .arrangement having a generally non-directional characteristic in a lgiven plane, comprising a' hollow supporting member, two ccnductive .ar-ms of .a length equalsubstantially to a .quarterr wavelength atlthe operating .frequency of said antenna arrangement, said arms extending in said plane and being rigidly connected to the supporting member at substantially one end thereof, a portion of one arm making an angle less than 180 with a corresponding portion of theother arm, each of said arms including a further portion, each said further portion being substantially parallel with the other, and means for energizing said arms at points on said arms equally spaced yfrom the point of rigid connection, said energizing means including within said supporting member conductor means further extending from one end of said supporting member to said spaced points.

'8. An antenna arrangement having a generally non-directional characteristic in a given plane, comprising a hollow supporting member, two conductive arms of a length equal substantially to a quarter wavelength at the operating frequency of said antenna arrangement, said arms extending in said plane and being rigidly connected to the supporting member at substantially one end thereof, a first portion on one arm 'making an angle less than 180 with a first portion on the other arm, a second portion on each said arm, each said second portion .being substantially parallel with-the other, anda third portion on each arm, said third portions making an angle less than 180 with each-other, andmeans for `ener-` gizing said armsat points on saidv arms `equally spaced from the point of rigid connection, said energizing means including within said supporting member conductor means further extending from one end 0f said supportingr member to said spaced points. f r

9. An antenna arrangement having a gener-v ly one end thereof, a portion of one of said arms making an angle of substantially 80 with lthe corresponding. portion of the other of said arms', and means for energizing said arms at points on said arms. equally spaced from the point of rigid connection, said energizing means including within said supporting member conductor means further extending from one end of said supporting member to said spaced points.

10. An antenna arrangement having agenerally non-directional characteristic iny a given plane, comprising a hollow supporting member, two conductive arms of a length equal substantially to a quarter wavelength at the operating 'frequency of said antenna arrangement, said arms extending `in said plane, said supporting member and said conductive arms being of streamlined cross-section, said arms being rigidly connected toward one end thereof to said support.- ing member at substantially one end thereof, and

means for energizing said arms at points on said j arms equally'sp'aced from the point of rigid connection, said energizing means including within said supporting member conductor means further extending from one end of said supporting member tosaid spaced points.

11. An antenna arrangement having a genernected to said supporting member at substantially oney end thereof, said supporting member and said conductive arms being of streamlined crosssection, the cross-section of each of said conductive armsA tapering down from said rigid connection, and means for energizing said arms at points on said arms equally spaced from the point of rigidy connection, said energizing means including within said supporting member conductor means further extending from one end oi said supporting member to said spaced points.

12. An aircraft antenna arrangement for operation in the neighborhood of a given ultrashcrt wave-length comprising ra strut member of conductive material extending generally vertically of the aircraft, a pair of antenna elements disally non-directional characteristic in a given'l posed inf a plane corresponding to a horizontal plane when the aircraft is in normal night, said antenna elements being galvanically inter-connected and rigidly supported toward one end thereof by said strut member and having portions thereof makin-g an angle less than 180 with each other, each said element having an overalllength of substantially a quarter of said wave-length, and means for coupling said elements to a wave-translating means, said coupling means ,including a pair of conductors withinsaid strut member, said conductors extending out the end of said strutmembers opposite the aircraft and being galvanically associated with said elements at points spaced from the point of support of said elements by said strut member.

13. An antenna arrangement according to claim 12, wherein said points of said galvanic association are spaced from said point of support a distance on the order of 0.02 to 0.06 of said wavelength.

, 14. An antenna arrangement according to claim 12., for aircraft having a fuselage of conductive material wherein said point of support is spaced from said yfuselage a distance on the order of 0.07 to 0.15 of said wave-length.

l5. An antenna arrangement according to claim 12, for aircraft having a fuselage of conductive material wherein said point of support is spaced from said fuselage a distance of the order of 0.07 to 0.15 of said wave-length, and wherein said strut` member extends from a portion ofy said fuselage relatively remote from the wings of the aircraft. v

` ANDREW ALFORD, 

